This invention relates to an arrangement by which stop-motion and variable-speed motion (Moviola) can be achieved on a tape recorder in which a scan of each head across the tape represents less than a complete television vertical field.
Conventional helical-scan video tape recorders have a plurality of heads or transducers each of which makes a single scan across the tape during an interval equal to one vertical field when either recording or playing back. Due to the motion of the tape, the angle of the scan across the tape is not the same as the angle of the track on the tape resulting from recording. In slow or stop-motion, or in fast motion of the tape, the scanning leaves one recorded track and may overlie another, depending upon the width of the guardband. At the time of such a crossing over, a low signal-to-noise condition occurs and a noise band appears on the raster on which the video is displayed. This noise band may be located in the middle of the raster, or the scan can be adjusted to divide the noise band to leave the center of the raster relatively noise-free whereby the noise bands are at the top and bottom of the raster.
Segmented-scan helical recorders scan across the tape in less than one full field, for example during one-half field. Thus two scans of the playback heads are necessary to produce one full field, and the transition between the heads occurs at the center of the field. Adjacent tracks in a segmented-scan recorder contain information derived alternately from the top and bottom of the raster, so crossing over of tracks by a scanning playback head results in gross distortion. It is desirable to provide slow, stop and fast motion in a segmented-scan helical tape recorder.